x86, perf: P4 PMU - Fix typos in comments and style cleanup

This patch:

 - fixes typos in comments and clarifies the text
 - renames obscure p4_event_alias::original and ::alter members to
   ::original and ::alternative as appropriate
 - drops parenthesis from the return of p4_get_alias_event()

No functional changes.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Link: http://lkml.kernel.org/r/20110721160625.GX7492@sun
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/include/asm/perf_event_p4.h b/arch/x86/include/asm/perf_event_p4.h
index 4d86c86..4f7e67e 100644
--- a/arch/x86/include/asm/perf_event_p4.h
+++ b/arch/x86/include/asm/perf_event_p4.h
@@ -133,7 +133,7 @@
 
 /*
  * In case of event aliasing we need to preserve some
- * caller bits otherwise the mapping won't be complete.
+ * caller bits, otherwise the mapping won't be complete.
  */
 #define P4_CONFIG_EVENT_ALIAS_MASK			  \
 	(p4_config_pack_escr(P4_CONFIG_MASK_ESCR)	| \